1. Field of the Invention
The present invention relates to a method of activating a compound semiconductor layer, necessary for manufacturing a compound semiconductor device for use in an optical device such as a blue-green light emitting device, a violet laser diode, a UV light emitting device, a laser diode or a transistor, to a p-type compound semiconductor layer.
2. Description of the Related Art
FIG. 1 is a sectional view showing the structure of a typical GaN-based optical device. As shown in FIG. 1, the GaN-based optical device is constructed such that a buffer layer 2 is formed on a sapphire substrate 1, a GaN layer 3, an n-GaN layer 4, an InGaN layer 5 and a P-type GaN layer 6 are sequentially stacked thereon, and then a p-contact layer 7 and an n-contact layer 8 are formed. The GaN optical device emits a blue, violet or green light, etc. and has a short-wavelength to provide full color display. Also, the GaN-based optical device can be applied to fields of high-capacity recording media for storing information. Also, since the GaN-based optical device exhibits excellent thermal properties, it can be applied to electronic devices capable of operating at a high temperature.
Nitride series compound semiconductors which are rapidly being developed in view of commercialization of short wavelength optical devices, entail a problem in manufacturing a p-type semiconductor, in contrast with other series materials including GaAs.
There are several well-known methods for growing a compound semiconductor layer, including a metalorganic chemical vapor deposition (MOCVD) method, a molecular beam epitaxy method and a hydride vapor method. In a state where a GaN series compound semiconductor has a layer grown by a metalorganic chemical vapor deposition (MOCVD) method, for example, and doped with p-type impurities, the GaN layer cannot be used as a device due to its high resistivity. This is presumably because hydrogen, serving as a reaction gas during growth of the layer is bonded with p-type impurities to be contained in a crystal and thus acts to prevent the p-type impurities from being electrically activated. In order to solve this problem, there has been proposed a method of increasing electrical conductivity using an electron beam. According to this method, electron beams are irradiated into a grown layer, thereby reducing resistivity. However, this method entails the problem of the generation of defects on the surface of the layer, thus deteriorating the performance of the device. Also, since electron beams cannot be irradiated over a large surface, the irradiated electron beams, having only up to a small area where the electron beams can reach, must be sequentially scanned over the entire surface. Thus, this method is not suitable for mass production. Alternatively, there has been proposed an annealing method. According to this method, the resistivity is lowered by annealing a grown layer at a temperature of 400xc2x0 C. or higher. However, with this method, since the grown layer must be exposed to a high temperature of 800-900xc2x0 C., the surface of the layer may be damaged. Also, the impurities contained in the layer may be diffused during growth, thus deteriorating the performance of the manufactured device.
To solve the above problems, it is a feature of the present invention to provide a method of manufacturing a compound semiconductor device, and more specifically, to a method of activating a compound semiconductor layer, which can reduce the resistivity of Mg-doped GaN, to a p-type compound semiconductor layer, by using electromagnetic waves.
It is another feature of the present invention to provide a method of activating a compound semiconductor, which can lower an annealing temperature to a p-type compound semiconductor layer by increasing an Mg content.
It is another feature of the present invention to provide a method of reducing the contact resistance between the compound semiconductor and electrode, which can reduce the contact resistance by increasing an Mg content, to accomplish the feature of the present invention. There is provided a method of manufacturing a compound semiconductor device using a compound semiconductor layer grown by a vapor phase epitaxy (VPE) method and doped with p-type impurities, and an electrode, comprising activating the compound semiconductor layer into a p-type compound semiconductor layer. By including the step of irradiating electromagnetic waves that can be absorbed into a p-type impurity doped compound semiconductor layer, onto the p-type impurity doped compound semiconductor layer.
In the present invention, it is preferred that the irradiating step is accompanied by annealing at a temperature of 350xc2x0 C. or higher. In particular, if the p-type impurity doped compound semiconductor layer used in the irradiating step is an Mg-doped GaN layer, the electromagnetic waves preferably have a wavelength shorter than 385 nm in the air.
Also, the compound semiconductor layer is preferably formed of one gallium nitride-based semiconductor material selected from the group consisting of InxGa1xe2x88x92xN, AlxGa1xe2x88x92xN, AlxGayInzN, BxGa1xe2x88x92xN, and BxAlyGazN
where 0xe2x89xa6xc3x97xe2x89xa61 in the case of a three-element mixed crystal compound, and x+y+z=1 in the case of four-element mixed crystal compound. Preferably, the p-type impurity of the compound semiconductor layer is at least one selected from the group consisting of Mg, Zn, Cd, Be, Ca and Ba.
To accomplish another feature of the present invention, there is provided a method of manufacturing a compound semiconductor device using a compound semiconductor layer grown by a vapor phase epitaxy (VPE) method and doped with p-type impurities, and an electrode, comprising, activating the compound semiconductor layer into a p-type compound semiconductor layer, by including the step of annealing the p-type semiconductor layer at a low temperature preferably of 200-850xc2x0 C. when the p-type impurity-doped semiconductor layer contains more than 5xc3x971019 cmxe2x88x923 of Mg as p-type impurities.
According to another aspect of the present invention, there is provided a method of manufacturing a compound semiconductor device using a compound semiconductor layer grown by a vapor phase epitaxy (VPE) method and doped with p-type impurities, and an electrode, comprising reducing the contact resistance of the compound semiconductor layer by including the step of doping the p-type impurities into the compound semiconductor layer at an amount of more than two times of the amount required when the resistivity of the p-type impurity-doped compound semiconductor layer is the lowest.